computation time

Hello everyone,When I used processor 2 2 1,I found it spend more time than one CPU,What can be the reason for this? Does anyone know?

Attachment	Size
Loop time with one cpu	704.01 KB
loop time with four cpu	57.42 KB

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LIGGGHTS® - User Forum

Philippe | Mon, 04/10/2017 - 12:25

system too small

My initial guess would be that your system is too small. In a system with 200 particles, the parallelization overhead is very likely to completely destroy your performance. Running a case in parallel only makes sense if you have at least several thousand particles per processor.

Bella | Mon, 04/10/2017 - 13:33

Thanks,but not work

Thanks for your reply,but I try 13705 atoms,it's still the same.loop time of 322.646 on 4 procs for 80000 steps with 13705 atoms
Loop time of 198.354 on 1 procs for 80000 steps with 13705 atoms.

mschramm | Mon, 04/10/2017 - 16:46

Communication Overhead?

Were you running one of the example cases? Which one?

What happens if you use a different processor arrangement? 1 2 2? 2 1 2? Letting LIGGGHTS choose?

Bella | Wed, 04/12/2017 - 10:24

The same phenomenon

Not example case,different processor arrangement is the same time